Field of the Invention
The present invention relates to a magnetic carrier to be used in a two-component developer for developing (visualizing) an electrostatic latent image (electrostatic charge image) by electrophotography, and to a two-component developer containing the magnetic carrier.
Description of the Related Art
In recent years, electrophotography has widely been employed in a copying machine, a printer, or the like. The electrophotography is required to be able to correspond to various targets such as a thin line, a small character, a photograph, and a full-color image. In addition, the electrophotography is required to be able to correspond to a high-quality image and a high-speed and continuous image output. Those demands are considered to increasingly grow in the future.
In order to satisfy those demands, light-weight composite particles each having a specific gravity of approximately 2.0 or more and 4.5 or less are often used as magnetic carrier particles in a magnetic carrier to be used in a two-component developer, because such composite particles are less liable to destroy toner particles even when an image is output at a higher speed and more continuously.
In addition, in order to output a high-quality image for a long period of time, it is important for the magnetic carrier to have such characteristics that an amount of charge to be imparted to toner hardly changes even when the magnetic carrier is used for a long period of time, and that an amount of charge to be imparted to toner hardly changes even when the magnetic carrier is subjected to an environmental change. In order to satisfy such characteristics, the magnetic carrier is required to have excellent durability.
As a technology for improving durability of the magnetic carrier, Japanese Patent Application Laid-Open No. H07-104522 discloses magnetic carrier particles obtained by forming a silicone resin coating layer containing a silane coupling agent or the like on surfaces of magnetic core particles (magnetic carrier core).
Japanese Patent Application Laid-Open No. S62-121463 discloses magnetic carrier particles obtained by treating surfaces of magnetic core particles (magnetic carrier core) with a coupling agent, and coating the surfaces with a silicone resin.
Japanese Patent Application Laid-Open No. H04-198946 discloses magnetic carrier particles obtained by treating surfaces of magnetic core particles (magnetic carrier core) with an aminosilane coupling agent, and forming on the surfaces a coating layer formed of a resin having a functional group capable of reacting with the aminosilane coupling agent.
In addition, from the viewpoint of weight saving of the magnetic carrier particles, magnetic carrier cores serving as constituents of the carrier particles each often have a configuration including a magnetic material and a resin (resin component).
A problem caused by using a resin in the magnetic carrier core is that an output image density and a color tint change through an environmental change from a low-humidity environment to a high-humidity environment. This seems to be attributed to moisture adsorbability of the resin.
Japanese Patent Application Laid-Open No. 2001-075315, Japanese Patent Application Laid-Open No. H09-127736, and Japanese Patent Application Laid-Open No. 2009-139707 each disclose a technology for specifying an adsorbed moisture amount of the magnetic carrier particles and suppressing the adsorbed moisture amount of the magnetic carrier particles.
However, the technologies disclosed as the technology for improving durability of the magnetic carrier in Japanese Patent Application Laid-Open No. H07-104522, Japanese Patent Application Laid-Open No. S62-121463, and Japanese Patent Application Laid-Open No. H04-198946 leave room for further improvement. In addition, the technologies disclosed as the technology for solving the problem caused by an environmental change from a high-humidity environment to a low-humidity environment in Japanese Patent Application Laid-Open No. 2001-075315, Japanese Patent Application Laid-Open No. H09-127736, and Japanese Patent Application Laid-Open No. 2009-139707 leave room for further improvement.